Irradiated rubbery elastomeric ethylene-alkyl acrylate interpolymers



United States Patent 3,274,086 IRRADIATED RUBEERY ELASTOMERTC ETHYL-ENE-ALKYL ACRYLATE WTERPQLYMERS James E. Potts, Millington, NJL,assignor to Union (Jarbide Corporation, a corporation of New York NoDrawing. Fiied June 29, 1962, Ser. No. 206,148 9 Claims. (Cl. 204-15914)This invention relates to synthetic rubbery copolymers and moreparticularly to rubbery copolymers of an ethylene-alkyl acrylatecopolymer having superior physical properties to the ethylene-alkylacrylate copolymers heretofore available which are useful as rubbersubstitutes. The invention is further directed to such copolymers havinglarge amounts inert fillers present.

Copolymers of ethylene and alkyl esters of acrylic acid are well knownin the art as are processes for producing these copolymers. In certainproperties these copolymers are superior to polyethylene and other knownethylene copolymers particularly in impact strength, tensile strength,ultimate elongation and ease of extrusion, i.e. lower softeningtemperatures and resistance to skinning and delamina tion.

However, in other properties these copolymers leave something to bedesired. The copolymers have a much lower crystallinity than doespolyethylene and for the most part are completely amorphous, thussubstantially lowering the use temperatures of the copolymer. Inaddition, as the amount of alkyl acrylate in the copolymer increases,not only does the polymer have lower softening temperatures but also thechain transfer elfects caused by the alkyl acrylate result in a lowermolecular weight weight. This substantial decrease in molecular weightof the copolymers has to some extent been corrected by decreasing thecatalyst concentration in the feed, but unfortunately this results in asubstantial decrease in the resultant conversion of the monomers tocopolymer.

This problem becomes more serious with increasing acrylate content inthe polymerization zone so that here totore in a tubular reactor system,for example, it has not been possible to prepare an ethylene-alkylacrylate copolymer having 15 percent or more combined alkyl acrylatewith a melt index below about 5, and with those copolymers having onlypercent combined alkyl acrylate it is nearly impossible to produce acopolymer of a melt index of less than 1.0. Consequently, theperformance normally achieved with other ethylene polymers has not beenpossible with the ethylene-alkyl acrylate copolymers. Low melt indexresins, such as those of 0.01 to 0.20 are generally necessary for manyapplications such as film orientation, cable and wire coatings, andother highly desirable applications where tensile and impact strengthsand ultimate elongation of a high order are more preferred.

Ethylene-alkyl acrylate copolymers containing from 15 to 40 weightpercent of ethyl acrylate have characteristics akin to rubbers andnatural elastomers but because of the aforementioned melt indexlimitation, presently available products do not have satisfactoryultimate tensile strength, yield strength, and elongation for commercialuse as rubber gum stocks and like uses. Further, because of thethermoplastic nature of the copolymers, they are lacking in elasticrecovery and infusibility, two important characteristics of commercialrubbers. Because of this, it is not possible to load these copolymerswith substantial quantities of inert fillers such as carbon black toexpand their possible use as rubber replacements.

Films of commercially available ethylene-alkyl acrylate copolymers showa decrease in solvent resistance and stiffness with correspondingincreases in acrylate content. When such films are formed by extrusion,an increase 3,274,086 Patented Sept. 20, 1966 in acrylate content alsoproduces an increase in optical haze level, as well as a decrease insurface gloss.

Thus, in many respects the presently available ethylenealkyl acrylatepolymers leave much to be desired.

It is therefore an object of this invention to provide an ethylene-alkylacrylate copolymer having a use temperature in the range of that forpolyethylene.

It is another object of this invention to provide an ethylene-alkylacrylate copolymer having a melt index substantially less than onedecigram per minute.

It is a further object of this invention to provide an ethylene-alkylacrylate copolymer having rubber-like physical characteristics, anduseful in the fields of applicability now limited to rubbers.

Still another object of this invention is to provide a film ofethylene-alkyl acrylate copolymer having good solvent resistance andstiflfness as well as low optical haze and high surface gloss regardlessof the mode of fabrication.

A still further object of this invention is to provide a process for theimprovement of properties of ethylenealkyl acrylate copolymer resins,particularly in the highly filled compositions to make themsuitablesubstitutes for rubbers.

Other objects of this invention will be apparent from the subsequentdisclosure and appended claims.

These and other objects are achieved by the present invention throughwhich it is now possible to make high molecular weight, low melt indexethylene-alkyl acrylate copolymers containing up to about 40 Weightpercent alkyl acrylate polymerized therein, which copolymers havesuperior tensile strength, elongation, elastic recovery and elevatedtemperature resistance. The copolymers produced herein can be tailoredto have any desired melt index or other combination of such propertiesdepending upon the ultimate or desired end use of the copolymer. By theuse of the present invention, it is now possible to produceethylene-alkyl acrylate copolymers useful as rubber substitutes. As amore desirable embodiment of the present compositions, it has now beendiscovered that they can be highly loaded with inert fillers to yieldtough elastomeric abrasion resistant rubber substitutes of excellentphysical properties.

These desirable results, it has been discovered, are secured by exposingan ethylene-alkyl acrylate interpolymer to ionizing radiation in amountsfrom about 0.5 to 50 megareps, and depending upon the melt index of thestarting copolymer, uniform products characterized by having a meltindex less than 1 decigram per minute are thereby produced. Filmsproduced from these copolymers are self-supporting and may be biaxiallyoriented. The polymers characterized by having an optical density permil thickness of 0.28 or less at 13.7 1. in the infrared spectrum aretruly elastomeric and are suitably employed as rubber stocks. Thesepolymers also are now characterized by having a use temperatureequivalent to polyethylene and superior to most other ethylenecopolymers in all physical properties. Copolymers of ethylene and alkylacrylates are by the present invention, made commercially useful forapplications where the presently available copolymers cannot be used.

As employed herein, the term alkyl acrylate" is intended to cover thealkyl esters of acrylic acid having in the alkyl moiety, groups havingup to about 12 carbon atoms. It is preferred in the practice of this.invention to utilize polymers made from the more simple acrylates, sucha methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate andlike acrylates having from 1 to 6 carbon atoms in the alkyl group.

It is further intended that the term interpolymer as used herein willinclude any copolymer, terpolymer, quadripolymer or other polymer, theconstitutents of such polymers being derived from the use of amultiplicity of alkyl acrylates copolymerized with each other and withethylene. This term is further defined as including copolymers having asmall or minor amount of a constituent therein other than alkyl acrylateor ethylene which may or may not be copolymerizable therewith but whichin any case will not substantially change the physical properties of theresulting copolymer at least insorfar as molecular Weight andcrystallinity are concerned, such as for instance, propylene, styrene,acrylic and methacrylic acid, butadiene and like monomers, as long asthe ethylene combined in the copolymer is present in a major amount. Thecopolymer must also contain from 5 to 40 weight percent of alkylacrylate polymerized therein. Of greatest interest are those copolymersof ethylene and ethyl or methyl acrylate which contain from about toabout Weight per cent of the alkyl acrylate combined therewith.Copolymers having 15 to 40 weight percent combined alkyl acrylate andcorrespondingly a high molecular Weight corresponding to a melt index ofless than about 0.4 decigram per minute at 190 C. (as measured byA.S.T.M. test Dl23857T) have not been made heretofore except by costlyand very impractical techniques.

' Thus there is no critical limitation in the melt index of the startingcopolymers other than that inherent in the methods for making them.However, extremely high melt indices of the starting copolymer are notparticularly desirable. It is preferable that the copolymers have a meltindex of less than about 70.0. Particularly effective results aresecured with copolymers having a melt index between 5 and 30, when theionizing radiation dosage is maintained between about 1 to 30 megareps.However, in the process of this invention the irradiation dosage is notso narrowly limited.

As stated heretofore these desirable results are accomplished by highenergy ionizing irradiation in doses from about 0.5 megarep to aboutmegareps, the dose being commensurate with the initial melt index of thecopolymer being irradiated and the desired final melt index of theirradiated copolymer. The lower molecular weight polymers as indicatedby a high melt index generally require a higher degree of irradiationthan those of initial high molecular weight.

Irradiation is effective at temperatures from C. to 200 C. and ispreferred between about 0 C. and 100 C. It is most convenient to utilizeambient temperature irradiation, that is, a sample being passed throughan irradiation beam at room temperature and the sample temperature isallowed to increase by the action of the irradiation until the desireddose is obtained.

The source of the ionizing radiation employed in this invention is notnarrowly critical. While the subsequent examples employ beta radiation(cathode emission) from a Van de Graatf electron accelerator, othersources of high energy electrons can be used. This Van de Graaifapparatus employed here and its operations have been fully described byF. L. Foster et al. in Nucleonics, October 1953, vol. 11, No. 10, pp.14-17 (McGraw-Hill Publishing Co., Inc., New York). Such radiation ismore properly called cathode radiation when obtained by suchelectromechanical means. As employed herein, one megarep or one millionreps (Roentgen equivalent physical) is that amount of radiationequivalent in energy delivered to 83.8 x 10 ergs per gram of polymer.

Other sources of high energy electrons (beta-radiation) such asradioactive isotopes and resonant transformer accelerators can beemployed, as well as sources of ionizing radiation such as gamma rays,X-rays, protons (hydrogen ions), dueterons (heavy hydrogen ions) orpositive ions such as alpha particles. Beta-radiation (high speedelectrons) obtained from radioactive isotopes such as strontium -yttrium90 equilibrium mixture can be used with similar results. Gamma rays,that is, electromagnetic radiation similar to light, but covering the 4Wave length range of 0.1 Angstrom unit to 0.001 A.U. may be obtained,for example, from cobalt 60 isotope or from a 2 million volt Van deGraafi electron accelerator equipped with a gold or tungsten target.Alpha particles can be obtained most easily from radio-isotopes such aspolonium 210.

It will be apparent that the term ionizing radiation as it is usedherein is intended to embrace gamma and X-rays as well. These latterrays, while they do not carry an electric charge, do in their passagethrough the polymer, eject electrons and the latter, being electricallycharged, are able to produce the radiation sufiicient for use in thisinvention. X-rays, electromagnetic radiation similar to light butcovering the wave-length range of 10 angstrom units (A.U.) to 0.1 AU. (1A.U. -10 cm.) can be obtained directly from an X-ray machine of aboutone-half million volts or more.

Exposure of the resin of ionizing radiation is best conducted bycontinuously passing it through the radiation field at a speed such thatthe residence time in the field is sufficient for the copolymer toabsorb the desired dose. Such continuous methods are particularlypreferred and are ideally suited to the practice of this invention.However, if desired, exposure can be similarly accomplished in batch orin semi-continuous operations.

It is not particularly critical that the copolymer employed in thisprocess be in any particular form during the exposure of theirradiation. The copolymer can be in pellet or granular form, or as acontinuous sheet, film, rod or other formed shape. If desired, thecopolymer can be directly irradiated at the outlet of the polymerizationreactor. For best results, the polymer preferably should be in a form orexposed under such conditions that all of the polymer will be exposed tothe same degree of irradiation and thus localized overexposed andunderexposed areas do not occur. Thus, pellets of a size of /s" to A"diameter or film or sheet stock of 0.5 mil to 250 mils thick can be usedwith excellent results in continuous exposure operation with a 2 mev.Van de Graafi elec tron accelerator as employed herein.

An outstanding advantage of the present invention is that it is nowpossible to prepare ethylene-alkyl acrylate copolymer rubbers havinggreatly improved tensile properties, excellent low temperatureflexibility, elongation of several hundred percent with excellentrecovery characteristics and outstanding resistance to ozone and oxygenattack due to the absence of significant amounts of internalunsaturation. These rubbers are both insoluble and infusible. T hepresence of large portions of carbon black does not prevent theattainment of these properties. The production of rubber in accordancewith this invention is shown in the appended examples.

A further outstanding advantage of this invention is that highly loadedrubbery compositions can be prepared which retain basically thedesirable properties of the copolymer in spite of the heavy loading offiller of 3050 parts filler per parts of copolymer. Especiallysurprising results are secured with carbon black as the filler. Regularor conventional polyethylene when filled and irradiated in a like mannergives a very weak and brittle product, entirely unlike the copolymers ofthis invention.

It is also contemplated herein that other fillers such as silica ordiatomaceous earth, stabilizers, antioxidants, and colorants, as well aspressing or filming aids as slip and anti-blocking agents and othermodifiers can be also included in these compositions to secure resultsas may be expected.

A preferred method for carrying out the process of the present inventionis by the technique employed in the following examples.

The equipment used in radiation treatment consisted of a Van de Graaitelectron accelerator, variable in voltage from 500,000 volts minimum to2.5 million volts maximum and variable in electron beam current from 0.1

microampere to 250 microarnperes. Samples of plastic ranging in widthfrom 0.001 inch to 1,5 inches and ranging in thickness from 0.5 mil to0.8 inch can be treated with this equipment. Molded plaques and sheetsvarying in thickness up to 0.8 inch, in width up to inches and in lengthup to 5 feet were irradiated with electrons by placing the samples on aconveyor belt moving at 40 inches 21 minute under the ionizing radiationbeam.

Pellets and powders were radiation treated by air-conveying the materialto an overhead hopper from whence the material is moved by gravity intoa vibrating feeder and thence onto a continuous conveyor belt movingunder the electron beam. The speed of this belt was variable from 2 to80 inches per minute.

Rolls of films were irradiated by placing the roll on a film winder,which was placed under the electron beam. The roll of film wasirradiated as it was unwound from the roll. The radiation dose wascontrolled by varying film speed, electron beam current and beam scanwidth.

Physical properties of the irradiated ethylene-alkyl acrylate copolymerswere measured by the following test method:

Vicat softening point-ASTM No. D1525-58T. Ultimate tensile strength-ASTMNo. D-412-51T. Percent elongationASTM No. D-4l2-51T. Gloss-ASTM No.D-523-53T.

Haze-ASTM No. D-1003-52.

Brittle temperature-ASTM No. D74644T.

Melt index-ASTM No. D-123 8-571.

Stress cracking-ASTM No. D-l693.

Tensile impact As reported in Modern Packaging, vol. 32, No. 1(September 1958), p. 147, by R. H. Carey and M. S. Nutkis.

Secant modulus-Similar to ASTM-D-638 except that specimen cut from die Adescribed in ASTM-D-412 rather than die required in D638. Calculated as100 times ratio of load (in pounds at 1% strain) to the arithmeticproduct of average width and average thickness in inches. Strain pointdetermined from stressstrain plot of automatic recorder,

Shrinkage-As percent shrinkage (average of machine and transversedirections) of film. The specimens were floated on a glycerine bath atspecified temperatures in the range 50-150 C. for 5 minutes. Dimensionalmeasurements were made at room temperature.

By method of the present invention it is possible to make ethylene-ethylacrylate copolymers having improved high temperature properties withoutdiminishing the good low temperature properties exhibited by presentlyavailable ethylene-ethyl acrylate copolymers. This is illustrated by thefollowing examples. Unless otherwise specified all parts and percentagesare by weight. All examples showing 0 radiation dose are controlexperiments and not part of this invention.

EXAMPLE I Plaques of an ethylene-ethyl acrylate copolymer containingbetween about 13 and 16 percent ethyl acrylate and having a melt indexof 4.5 averaging about A to /s" in size were irradiated with 2 millionvolt electrons using the Van de Graaff accelerator, with the resultsshown below obtained from sample plaques, 6 inches by 8 inches by 40mils thick.

completely in /2 hour. The third showed no change in dimensions after 4hours at 158 C. and retained substantially all of its initial physicalproperties.

EXAMPLE II An ethylene-ethyl acrylate copolymer containing about 15weight percent ethyl acrylate and having a melt index of 4.0 wascompression molded into plaques 6 inches by 8 inches by 40 mils thick.Samples of the same copolymer was hot-blended at 125 C. with 33 parts ofcarbon black per 100 parts of copolymer; the mixture was also moldedinto plaques of the same size. Plaques of the unfilled copolymer plaquesand the carbon black filled copolymer were irradiated with two millionvolt electrons to a radiation dose of 25 megareps. Properties of thefilled and unfilled, radiated and unirradiated plaques were compared.

The unirradiated plaques, with or without carbon black melted completelyat about C. Irradiation of the unfilled copolymer produced a producthaving a stiffness (secant modulus at 1 percent elongation) of aboutpsi. up to about 300 C. whereas the black-filled irradiated sample had astiffness of about 200 p.s.i. at about the same temperature.

EXAMPLE III An ethylene-ethyl acrylate copolymer containingapproximately 35 percent ethyl acrylate and having a melt index of 70.5was compression molded in plaques 6 inches by 8 inches by 40 mils thick.Additionally the same copolymer was blended with 43 parts of carbonblack and 100 parts of carbon black per 100 parts of copolymer andmolded into plaques of the same size. Some of the samples wereirradiated to a dose of 25 megareps. Some of the unfilled plaques weregiven a dose of 50 megareps. The results were identical with those ofthe previous example in that the stiffness was improved at elevatedtemperature with increasing irradiation dose and with increasing carboncontent.

The irradiated copolymer showed a 14 percent hysteresis loss at 25megareps dose whereas the unirradiated control sample was too soft to besubject to this measurement. The stress-strain curves for the samplesshowed no adverse effects from irradiation. The results of permanent settensile strength and percent elongation of the 25 megarep samples areshown in the following table:

Carbon black Radiation Percent Tensile parts per 100 dose, permanentstrength, Percent parts resin megareps set at 100% p.s..i. elongationelongation 1 Sample too soft to measure.

EXAMPLE IV An ethyleneethyl acrylate copolymer, containing about 12percent ethyl acrylate, having an initial melt index of 4.0 wascompression molded into plaques 6 inches by 8 inches by 40 mils thickand the plaque irradiated with 2 million volt electrons with the resultsshown below:

Tensile Vicat Ultimate Percent 65 Melt Ultimate Brittle Dose, Impact Soten g Tensile afi Dose Index, Tensile Percent temperature,

s p t g o t, s Elonsatlon Megareps 0. Strength, Elongation 80 C.

p.s.1. P.S.l. p.s.i.

Other data pertaining to irradiated, unfilled ethyleneethyl acrylatecopolymers are given below. These prove Radiation Tensile BrittlenessDose, Ultimate Percent Impact, Temperamegareps Tensile Elongationfoot-pounds ture, C

per inch 3 Similarly, for a copolymer having a melt index of 47.5produced from a comonomer feed containing 1.24 mole percent ethylacrylate and containing about 25 percent by weight ethyl acrylate in thecopolymer, the results are:

Radiation Tensile Brittleness Dose, Ultimate Percent Impact,Temperamegareps Tensile Elongation foot-pounds ture, C

per inch 3 Similarly, for a copolymer having a melt index of 70 produced[from a comonomer feed containing 1.87 mole percent ethyl acrylate,containing about 33% by weight of ethyl acrylate in the copolymer, theresults are:

Radiation Tensile Brittleness Dose, Ultimate Percent Impact,Temperamegareps Tensile Elongation foot-pounds ture, O

per inch 3 1 Too soft to measure.

Carbon blackfilled ethylene-ethyl acrylate compositions have greatlyimproved low-temperature properties after irradiation which are superioreven to similarly irradiated carbon black filled polyethylene. This isshown by the following example:

EXAMPLE V Comparison of irradiated DYNH carbon black mixtures andirradiated ethylene-ethyl acrylate copolymer-carbon black mixtures(Polyethyl Ethyleneene) DYN H ethyl acrylate copolymer Mole percentacrylate in feed 1. 0 Percent acrylate 0 20 Melt Index Initially 2 26. 5Parts carbon black per 100 parts resin 50 50 Radiation dose, megareps 2025 Final Melt Index Ultimate Tensile strength, p.s.i. 23 C 2, 400 1, 090Percent elongation 215 550 Brittle temperature, C -64 1 Too stiff tomeasurebasically zero melt index.

Following the process of the present invention it is possible for thefirst time to obtain ethylene-ethyl acrylate copolymers containing from5 to 40 percent by Weight combined ethyl-acrylate having a melt indexbelow about 0.5 decigram per minute. These copolymers which areillustrated in the five examples could be readily molded and extrudedinto any desired shape yielding smooth glossy surfaces.

EXAMPLE VI Three samples of an ethylene-ethyl acrylate copolymercontaining about 15 weight percent combined ethyl acrylate and having amelt index of 4.02 decigrams per minute at 190 C., were irradiated inthe form of approximately /8 inch cube pellets, with a radiation dose oftwo, four, and six megareps using the equipment for handling pelletsdescribed earlier. The belt speed was 20 inches per minute, and the beamcurrent was 250 microamps. The melt index of the first product was0.735, of the second product was 0.065, and of the third product waszero. The first two products could be molded at temperatures of C-300"C. to give plaques ha ving smooth, glossy surfaces.

EXLAMPLE VII An ethylene-ethyl acrylate copolymer containing about 20weight percent combined ethyl acrylate, and having a melt index of 26.5in the form of compression molded plaques, was irradiated with 2 millionvolt electrons to a dose of 2 megareps, which reduced its melt index to9.18. A radiation dose of 4 megareps reduced its melt index to 4.96. Adose of 6 megareps reduced the melt index to 0.14. After 8 megarepsdose, the melt index was 0.046. The product resulting from a dose of 10megareps had a zero melt index and Was molded or extruded only withdifiiculty. However, the products resulting from irradiation which hadmeasurable melt indices were easily molded by compression or injectionmolding to give molded pieces having attractive glossy surfaces ofimproved transparency compared to pieces from the unirradiated polymer.The tensile strength of the molded pieces increased with increasingradiation dose.

EXAMPLE VIII Plaques molded from an ethylene-ethyl acrylate copolymercontaining about 25 weight percent combined ethyl acrylate and having amelt index of 47.4 were redueed in melt index by irradiation as follows:2 megareps, 25.2 melt index; 4 megareps, 18.0 melt index; 6 megareps,8.13 melt index; 8 megareps, 1.92 melt index; 10 megareps, 0.17 meltindex; 16 megareps, 0.00 melt index. All of the above products, save thelast, could be molded or extruded into useful shapes by compression orinjection molding at temperatures below 200 C. The zero melt indexsamples were molded with difficulty at temperatures above 200 C., andwere lacking smooth surfaces.

EXAMPLE IX A sample of ethylene-ethyl acrylate in the form of castsheet, containing about 35 percent combined ethyl acrylate, having amelt index of 70.5, was reduced in melt index by treatment with 2million volt electrons as follows: 2 megareps dose, 30.1 melt index; 6megareps, 12.2 melt index; 10 megareps, 0.756 melt index; 12 megareps,0.533 melt index; 14 megareps, 0.0 melt index. All the irradiatedsamples could be fabricated by molding or extruding to give attractivepieces having greatly improved tensile strengths compared with thecontrol which was of the consistency of putty.

It is also now possible to make ethylene-ethyl acrylate copolymersessentially free from environmental stress cracking (as shown inExamples X and XI) and having superior impact strength to the presentlyavailable ethylene-ethyl acrylate copolymers (as shown in Examples 1,XII, and XIII).

EXAMPLE X An ethylene-ethyl acrylate copolymer containing 5-6 percentcombined ethyl acrylate and having a melt index 9. of 4.2 was moldedinto 125 mil thick plaques which were annealed 7 days at 70 C. Otherplaques of the same material were irradiated to doses of 5, 10 and 20megareps and then aged 7 days at 70 C. The plaques were submitted forenvironmental stress crack resistance tests in Igepal. These results andother properties are tabulated below:

strength, low brittleness temperature resin from carbon filledpolyethylene whereas surprisingly, it is possible to secure them fromthe ethylene-alkyl acrylate copolymers of this invention.

As was previously stated, ethylene-ethyl acrylate copolymers produced inaccordance with the present invention may be biaxially oriented toprovide films which are Radiation Tensile Percent Tensile Irn-Brittleness Stress Crack Resistance dose, Strength, Elongapact, foot-Tempcra- Hrs. to Fail megareps p.s.i. tion pounds/inch ture, 0.

1,895 700 439 -80 100% failure in 4 hrs. 2, 687 720 654 80 N failure in21 days. 3, 079 680 846 -80 0. 3,184 515 1, 044 80 D0.

EXAMPLE XI greatly improved in optical clarity as shown by higher Asample of 1.5 mil tlhick film made, by blown tubular extrusion process,from an ethylene-ethyl acrylate copolymer containing about percent ethydacrylate and having a melt index of 5 was irradiated with 2 million voltelectrons, using a shuttle conveyor to various radiation doses andtested for tensile impact strength. The results were as follows:

Tensile Impact Strength Radiation dose, (Foot Pounds/Cubic Inch)megareps Machine Direction Transverse Direction The samples which hadbeen irradiated would not dissolve in boiling toluene. The unirradiatedresin dissolved easily.

EXAMPLE XII Polyethylene and an ethylene-ethyl acrylate copolymer wereeach mixed With carbon black in the proportions of 3 parts resin to 1.5parts of black. Eadh blend was compression molded into 40 mil plaques,some of which were irradiated at varying dose from 5 to -25 megareps.Half of the plaques were annealed 7 days at 70 C. in a forced air oven.All of the plaques were subjected to measure ments of various physicalproperties. The results are summarized in the following table:

The dramatic effect of this process is observed on the tensile impactstrength secured on the copolymer having combined acryllate. Theresulting product has more than twice the impact strength than thepolyethylene and a brittleness temperature below 50 C. The highbrittleness temperature of the carbon black loaded polyethylene makes itcommercially useless for many applications Whereas the copolymer is verydesirable. In other Words, it is not possible to secure a highlyelastic, high impact gloss and lower haze levels and which demonstrateC. shrinkage adequate for poultry shrink packaging. Presently availableethylene-ethyl acrylate copolymers can not be biaxially oriented in acontinuous manner at temperatures which will yield the same desiredproperties and improvements. These improvements are shown in thefollowing two examples (Examples XIII and XIV).

EXAMPLE XIII A sample of ethylene-ethyl acrylate copolymer in the formof an extruded tubular film 8 mils thick, containing 10 percentacrylate, having a melt index of 4.7 and a density of 0.9205 was given aradiation dose of 5.0 megareps. The final melt index was 0.12. Thisproduct was biaxially oriented in a continuous manner at a temperaturejust below the softening point of the resin to an expansion ratio of3.3/5. The shrinkage at 90 C. of this film was 18 percent machinedirection, 34 percent transverse direction. Its 45 degree gloss was 72percent and its haze was 2.6%. Unirradiated tubular film of this productcould not be biaxially oriented.

EXAMPLE XIV Polyethylene and three different ethylene-ethyl acrylatecopolymers were subjected to ionizing radiation of 25 megareps. Each ofthe copolymers were irradiated with and without carbon black; theresults are shown in the following table:

Mole percent Melt Index Optical Den- Parts E-lack/ Percent Set acrylatein before sity per mil pts. resin at 100% Elon- Feed Irradiation at 13.7micron gation after Irradiation 1. 8 0. 405 0 100 4.0 0. 278 0 17. 5 4.0 0. 278 33 26. 0 26. 5 0.17 0 20 26. 5 0.17 43 20 70 Nil 0 10. 7 70 Nil43 10. 5

It is to be noted that the disappearance of the 13.7 absorption bandwhich normally indicates crystallinity, on the examples of 1.87 molepercent acrylate (3035 percent .by weight combined et hyl acrylate) isindicative of a rubbery amorphous polymer, and the 10% set afterelongation proves that a good rubber is obtained. This is equivalent tonatural rubber.

EXAMPLE XV A sample of ethylene-ethyl acrylate copolymer, having a meltindex of 68, containing about 30-35 percent by weight combined ethylacrylate and being substantially free from crystallinity as demonstratedby the absence of an absorption band at 13.7 microns when this productwas analyzed by infrared absorption spectroscopy, was blended at C. in aBambury mixer with 43 parts furnace type carbon black per 100 parts ofresin and compression molded into fiat sheets 6 inches by 8 inches by 40mils thick. This material bad an ultimate tensile strength of 330 p.s.i.at 23 C. and an elongation at break of 40 percent. Tensile set at 100percent elongation could not be determined on this product, since itwould elongate only 40 percent, and then took a permanent set. Thematemperatures to a final melt index of 0.12 decigram per minute. Thisfilm was biaxially oriented at just below its softening point to anoriented film size of 0.30.6 mil and a fiat width of 10 inches. Themachine driection stretch was 3.3/1 and the transverse direction was5.0/1.

terial was so lacking in tenacity that its low temperature 5 Afterorientation and cooling, the film showed a shrinkbrittleness could notbe determined. Other plaques of age at 90 C. of 18 percent in themachine direction and this same product were irradiated with 2 millionvolt 34 Percent the transverse difflction, and at of electrons from aVan de Graaff accelerator by placing 64 Pefoeflt in i116 machinedirection and 73 P in the plaques .on a shuttle conveyor belt andpassing the the transverse direction. Its gloss at an angle of 45desamples under the electron beam at a speed of 40 inches grees 72Percent and its haze Was Percent? per minute, at a b id h f 12 i h d .abeam cur- The irradiated, biaxially oriented film had a tensile rent of250 microamps a t l d f 25 megafeps strength in the machine direction of7915 p.s.i. and in the The product had a melt index of 0.00, an ultimatetensile transverse direction of 8929 p.s.i. It had an elongationstrength of 1080 p.s.i. at 23 C., and an elongation of 300 15 at breakof 233 percent in the machine direction and 107 percent i h a Zeropercent t il et t 100 percent 1 percent in the transverse direction. Ithad a tear strength gation. The 80 percent brittleness temperature ofthis in 19 grams P in the machine direction and 13 grams d t was 68 Q Thi l hibi d h prgpper mil in the transverse direction. Its oxygentranserties of an insoluble, infusible snappy rubber. Regular missionWas 672 cc./100 m. 24 hrs/mi The film polyethylene treated in the samemanner with the same 20 had an impact Strength of inch Pounds P mil andcarbon black loading gives a weak brittle product at aspectraltransmission of 3811101163- 23 C By way of comparison, unirradiated filmidentical to EXAMPLE XVI that specified above could not be continuouslybiaxially oriented.

An ethylene-ethyl acrylate copolymer, contalniflg 25 25 The presentinvention is not limited to ethylene-ethyl Percent Qthyl acrylate,hflvlng a g Index of was acrylate copolymer but also is applicable withother ethylblended 111 a y IIllXel' at 125 for 10 minutes ene-alkylacrylate copolymers. This is shown in the with 48 parts of fiurnace typecarbon black per 100 parts f ll i eXamp1eS resin and compression moldedinto plaques 6 inches by 8 inches by 40 mils thick. Some of these wereirradiated to EXAMPLE XIX d0$ 65 of 7, 10 and 25 megareps using thepreviously A sample of ethylene-butyl acrylate copolymer conscribedprocedure. The physical properties were as -foltaining 29 weight percentbuty l acrylate and having a 10WSI melt index of 1.3 decigrams perminute, was compression Ultimate Tensile Tensile Sct Brittle SecantDose, Strength at 100% Temp. 80% Modulus at Megareps Tensile, Elongaat100% Elongation C.) 1% Elongap.s.i. tron, Elongation tion, p.s.i.

percent EXAMPLE XVII r molded into a 10 mil film and subsequentlyirradiated to To further show the effect of irradiation on crossa dose 910 megareps' This irradiated film was tested linking of the Subjectcopolymer, an ethy1ene ethy1 any for tensile strength, secant modulus at1.0 percent elongalate copolymer, containing 3 to 5 weight percent oftron and elongation at break. The results are shown in bined acrylate,having a melt index of 12 and produced the table below, along with thepropertles of the unirradlfrom a feed gas containing 0.22 mole percentethyl acryatfid copolymerlate, was subjected to various radiation dosesand the product tested for percent insolubles in boiling toluene.

Each of the irradiated products had a zero melt index. The test resultsare as follows, Tensile Percent Secant Modulus Radiation Dose, Strength,Elongation at 1 percent Dose, lrnegareps: Percent insoluble in boilingtoluene megareps at break elongation 0 Negligible 5 24.6 s 42.0ibIIIIIIIIIIIIIIIIIII 1488 $38 3333 12 55.9 16 65.1 20 70.6

EXAMPLE XVIII The unirradiated films disintegrated immediately onimmersion in boiling toluene and dissolved completely 55 32 ggifiy gg zggi g gfgg gi zgggi i ffi within 15 minutes. The irradiated filmsremained intact form of film a product can be produced which can be bii;i the g g fi and dld not dissolve axially oriented by stretching belowthe melting point of Comp 6 e yeven on pro eatmg' the polymer sufiicientto align the molecules of the poly- EXAMPLE XX mer without breaking theproduct being stretched.

An ethylene-ethyl acrylate copolymer containing 10 A sample ofethylene'z'ethyl hexyl acrylate copolymer weight percent combined ethylacrylate, having a melt containing 21 Weight Pfircent y heXyl acrylateand index of 4.7 decigrams per minute and a density of 0.9205 having amelt indeX 0f 8 Was compression molded into a gram per cubic centimeterwas extruded at 310 F. into 10 mil film and irradiated to a dose of 25megareps. The a seamless tubular film 8 mils thick with a flat width of2 results are shown in the following table along with the inches. Thefilm was irradiated to 4 megareps at ambient properties of theunirradiated copolymer.

The unirradiated films disintegrated immediately on immersion in boilingtoluene and dissolved completely within 15 minutes. The irradiated filmremained intact briefly under the same conditions and did not dissolvecompletely even on prolonged heating.

EXAMPLE XXI A sample of the ethylene-Z-ethyl hexyl acrylate copolymer ofExample XXII was compression molded into a 10 mil film and subsequentlyirradiated to a dose of 1 megarep. The starting copolymer had a meltindex of 8 decigrams .per minute, and after irradiation to a dose of 1megarep it had a melt index of 2.2. A radiation dose of 2 megarepsreduced its melt index to 0.61. A dose of 4 megareps reduced the meltindex to 0.04. A dose of 8 megareps reduced the melt index to 0.008. Theproduct resulting from a dose of 10 megareps had a zero melt index andwas molded or extruded only with diificulty. The irradiated productshaving measurable melt indices were easily molded by compression orinjection molding to give molded pieces having improved transparencycompared to pieces molded from unirradiated copolymer.

What is claimed is:

1. A method for producing ethylene-alkyl acrylate copolymers of 10W meltindex which comprises the step of irradiating a normally solidethylene-alkyl acrylate interpolymer having an initial melt indexbetween 1 and 70 and containing from 5 to 40 weight percent of combineda-lkyl acrylate and a major amount of combined ethylene with ionizingradiation in an amount from about 0.5 to 50 megareps commensurate withthe initial melt index of the copolymer such that the resultingirradiated copolymer has a melt index less than 1.0.

2. A method for producing ethylene-alkyl acrylate cpolymers having amelt index less than 1.0 which comprises irradiating a normally solidethylene-alkyl acrylate interpolymer having a melt index between aboutand 30 and containing from 5 to 40 weight percent of combined alkylacrylate and a major amount of combined ethylene with ionizing radiationin an amount from about 1 to 30 megareps commensurate with the initialmelt index of the starting copolymer such that the irradiated copolymerhas a melt index less than 1.0.

3. A method according to claim 2 wherein the alkyl acrylate is ethylacrylate.

4. A method for producing rubbery elastomeric ethylene-alkyl acrylateoopolymers having melt indices less than 1.0 which comprises irradiatingan ethylene-alkyl acrylate interpolymer having an initial melt indexbetween 1 and and containing from 15 to 40 weight percent combined alkylacrylate and a major amount of combined ethylene with ionizing radiationin an amount between about 1 to 30 megareps commensurate with theinitial melt index of the copolymer such that the irradiated copolymerhas a melt index less than 1.0.

5. A method according to claim 4 wherein the alkyl acrylate is ethylacrylate.

6. An irradiated rubbery elastomeric ethylene-:alkyl acrylateinterpolymer having a melt index less than 1.0 and containing firom 15to 40 weight percent combined alkyl acrylate, and a major amount ofcombined ethylene and an optical density per mil thickness less than0.28 at 13.7,LL wave length.

7. An ethylene-alkyl acrylate copolymer of claim 6 wherein the alkylacrylate is ethyl acrylate.

8. An irradiated carbon-filled rubbery composition containing from 30 to50 parts of carbon per parts by weight of an ethylene-alkyl acrylateinterpolymer having a melt index less than 1.0 and containing from. 15to 40 weight percent combined alkyl acrylate and a major amount ofcombined ethylene and an optical density per mil thickness less than0.28 at 13.7;i Wave length.

9. A carbon filled composition of claim 8 wherein the alkyl acrylate isethyl acrylate.

References Cited by the Examiner UNITED STATES PATENTS 3,090,770 5/1963Gregorian 204154 3,097,150 7/1963 Rainer et al. 204154 OTHER REFERENCESLawton et al.: Nature, vol. 172, pages 76 and 77 (July 1 1, 1953).

MURRAY TILLMAN, Primary Examiner.

JOHN R. SPECK, Examiner.

H. S. WILLIAMS, W. L. BASCOMB, N. F. OBLON,

Assiszant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,274,086 September 20, 1966 James E. Potts It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 1, line 15, before "inert" insert of line 33 for "weight", firstoccurrence, read polymer column 4, line 18, for "of", second occurrence,read to column 7,

second table, third column, line 1 thereof, for "500" read 400 Signedand sealed this 29th day of August 1967,

( L) Attest:

1 ERNEST w. SWIDER EDWARD -J. BRENNER Attcsting Officer Commissioner ofPatents

1. A METHOD FOR PRODUCING ETHYLENE-ALKYL ACRYLATE COPOLYMERS OF LOW MELTINDEX WHICH COMPRISES THE STEP OF IRRADIATING A NORMALLY SOLIDETHYLENE-ALKYL ACRYLATE INTERPOLYMER HAVING AN INITIAL MELT INDEXBETWEEN 1 TO 70 AND CONTAINING FROM 5 TO 40 WEIGHT PERCENT OF COMBINEDALKYL ACRYLATE AND A MAJOR AMOUNT OF COMBINED ETHYLENE WITH IONIZINGRADIATION IN AN AMOUNT FROM ABOUT 0.5 TO 50 MEGAREPS COMMENSURATE WITHTHE INITIAL MELT INDEX OF THE COPOLYMER SUCH THAT THE RESULTINGIRRADIATED COPOLYMER HAVING A MELT INDEX LESS THAN 1.0.